Because he looks clueless on the bench and, from what I recall, there wasn't much of a turn-around when he was named head coach. Even the worst of head coaches can usually squeeze a half-decent streak out of their team at the beginning (see Rick Kehoe).
Gallant may not have a playoff team on paper, but he's still got plenty of talent and did nothing with it (again, as I recall) late last season.
But I'd have to give Renney the nod here. As if his comments on Messier's spear didn't do it for me, his actions of double-shifting Dale Purinton in a close game certainly did.
Brian Sutter, especially given that he hired Butch Cassidy (who would likely hold this distinction if anyone is dumb enough to hire him again) as an assistant. Curt Fraser would be #1 with a bullet if he ever somehow found a coaching job again.